1. Field of the Invention
The present invention relates to a plastic lens, and more particularly to a plastic lens formed of a urethane-based resin having a UV absorptive function.
2. Description of the Prior Art
Plastic lenses have various advantages as compared with glass lenses. For example, plastic lenses have a relatively light-weight and are less vulnerable to breakage in comparison with glass lenses. Further, plastic lenses are colorable, and precision molding thereof can be easily carried out. In view of these advantages, in recent years, plastic lenses are widely used for optical lens products such as an eye-glass lens, camera lens, Fresnel lens, lenticular lens, prism and the like.
Among these plastic lenses, a plastic lens formed of a urethane-based resin has less optical distorsions and it has a high safety due to its excellent transparency and superior impact resistance, so that such a lens is preferably used as an eye-glass lens or the like.
In addition, plastic lenses to which UV absorptive function (UV absorptive power) is imparted have been proposed in order to protect the crystalline lens, the retina and the like from the injury by the UV. The UV absorptive function is imparted, for example, by forming a plastic lens using a resin material for plastic lens which has UV absorptive function in itself, or by providing a coating layer formed of an UV absorbent having UV absorptive function on the surface of the molded plastic lens.
However, in these methods, there have been problems such as yellowing of the lens and changes in the index of refraction of the lens due to the own color (yellow) of the resin material for the plastic lens or the UV absorbent. Moreover, there have also been such problems as the deterioration in the mechanical strength and the deterioration of transparency of the lens due to the addition of the UV absorbent and the addition of a color complementing agent which is added for the purpose of adjusting the yellowing to be caused by the UV absorbent.